Electromagnetically actuated fluid control valves, particularly relatively small valves of this type, have widespread use in the application of fluid control. Some examples of applications for this type of valve are for ink jet printing, dye patterning on textile substrates, and precision fluid control in medical and HVAC applications. The most common type of fluid control valve presently in use is a solenoid valve which includes a high permeability straight core with a centrally disposed air gap and a coil wrapped around the core. The disadvantage of this type is that the closed lines of flux must pass through the low permeability space outside of the coil which adversely affects the development of force across the air gap.
German Pat. No. 24 40 565 discloses a nozzle flap valve in which a core, yoke and flap form a magnetic circuit. A nozzle pipe extends through the magnetic core and into the air gap so the air gap is obstructed and the magnetic flux is not closely confined and further there are several interruptions in the loop of the magnetic circuit.
Fischer et al. U.S. Pat. No. 4,196,751, Morris U.S. Pat. No. 4,759,528, Nanbu et al. U.S. Pat. No. 4,848,727 and Iljin U.S. Pat. No. 4,905,962 disclose pot cores in which the coil is wound on a central leg and includes flux in a circular outer path and back to the center leg which is a magnetic path of non-uniform cross-section. These types of solenoid designs result in the uniform dispersion of flux lines as they pass from the solenoid core into the permeable material surrounding the coil. The armature must be of equal diameter to the permeable material outside of the coil in order to complete the magnetic path. This results in a greater armature mass, and consequently a slower switching speed, for a given force, than could be obtained if the armature's size was directly related to the cross sectional area of the solenoid core.
Holloman U.S. Pat. No. 3,589,672 discloses an armature carried on a resilient non-magnetic strip and actuated by coils on a pair of parallel legs of a U-shaped core.